Adsorption and diffusion characteristics on polymer/liquid crystal interface

Viscoelastic properties of liquid crystal (LC) on polymer/liquid crystal interface are investigated using a quartz crystal microbalance (QCM). The time-evolution curve of the resonant frequency shift (-Δf) and the resonant (ΔR) resistance shift of QCM for the LC on polystyrene (PS) surface involves four different stages: in the first and third stages, both -Δf and ΔR are increased, whereas in the second and fourth stages, -Δf is increased while ΔR was almost constant. These results indicate that the first stage and third stage of adsorption should be characterized mainly by viscosity change, while the second stage and fourth stage can be ascribed to the adsorption and/or the formation of an elastic medium. The increase of viscosity in the first stage should be associated with the director re-orientation of liquid crystals from lateral to normal. The second stage involves the formation of a solidified layer. The third stage exhibits an increase in the viscosity due to the diffusion of the polymer chains in the liquid crystal to form a viscoelastic interfacial layer. In the fourth stage, the interfacial layer should be solidified (viscoelastic to elastic). The thickness of thus formed interfacial layer is estimated to be 200 nm on PS and 50 nm on hydroxypropyl cellulose, depending on the miscibility.